Perfluorocyclobutane (C-318, b.p. -6.degree. C.) is a valuable material which can be used as a propellant, etch gas, and fire extinguishant. This compound is typically made by cyclodimerization of tetrafluoroethene (TFE) or is recovered as a by-product from the manufacture of TFE. As a result C-318 may be contaminated with unsaturates such as E- and Z-perfluoro-2-butene (i.e., CF.sub.3 CF.dbd.CFCF.sub.3 or FC-1318my) and perfluoroisobutene (i.e., (CF.sub.3).sub.2 C.dbd.CF.sub.2 or PFIB or FC-1318mmt). These compounds, especially the latter, are highly toxic and must be removed prior to commercial use. FC-1318's are difficult to separate from C-318 by distillation as the boiling points are similar.
Perfluorobutane which can be used as an etch gas has typically been prepared by cumbersome methods. One such preparation disclosed by J. Burdon et al., J. Fluorine Chem., 40 (1988) 283-318 involves the fluorination of butane by cobalt trifluoride to yield at least 51 compounds, among which perfluorobutane was identified.
U.S. Pat. No. 5,001,287 discloses a process for treating an impure mixture consisting essentially of at least one olefinic impurity and at least one saturated halocarbon by contacting the mixture with a source of hydrogen in the presence of a hydrogenation catalyst. The saturated halocarbon includes perfluorocyclobutane and the catalyst includes Group VIII metals.
There is a need for alternative methods of purification.